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Abstract:

A process is disclosed for the conversion of cellulosic biomass, in
particular ligno-cellulosic biomass. The process comprises heating the
biomass to a conversion temperature in the range of from 200 to
500° C. in the presence of a catalyst system. The catalyst system
comprises a basic functionality comprising an alkali metal component and
a multivalent metal component. The catalyst system optionally further
comprises an acidic component.

Claims:

1. A process for the catalytic pyrolysis of cellulosic biomass, said
process comprising heating the cellulosic biomass to a conversion
temperature in the range of from 200.degree. C. to 500.degree. C. in the
presence of a catalyst system, characterized in that the catalyst system
comprises a basic functionality, said basic functionality comprising an
alkali metal component and a multivalent metal component.

2. The process of claim 1 wherein the multivalent component comprises a
divalent metal, a trivalent metal, or a combination of a divalent metal
and a trivalent metal.

3. The process of claim 1 or claim 2 wherein the multivalent metal
component comprises a hydrotalcite, a hydrotalcite-like material, an
anionic clay, a mixed metal oxide, or a mixture thereof.

4. The process of any one of the preceding claims wherein the alkali
metal component comprises an alkali metal carbonate.

5. The process of any one of the preceding claims wherein the alkali
metal component and the multivalent metal component are combined in a
catalyst particle.

6. The process of any one of the preceding claims wherein the catalyst
system further comprises an acidic component.

18. The process of any one of the preceding claims wherein the cellulosic
biomass is of aquatic origin.

19. The process of any one of claims 1-17 wherein the cellulosic biomass
comprises a ligno-cellulosic biomass.

20. The process of claim 19 wherein the lignocellulosic biomass is an
energy crop material, an agricultural waste material, or a forestry waste
material.

21. The process of any one of the preceding claim wherein the catalyst
system comprises catalyst particles, said catalyst particles comprising
all components of the catalyst system.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates generally to a multi-functional catalyst
system for the conversion of biomass, and more particularly to such a
system for the catalytic pyrolysis of cellulosic biomass.

[0003] 2. Description of the Related Art

[0004] Cellulosic biomass, in particular ligno-cellulosic biomass, is an
abundantly available source of energy. Many attempts have been described
to convert cellulosic biomass to liquid fuel. In general, the conversion
of cellulose to liquid fuel comprises depolymerization of the cellulose;
cracking of the depolymerization reaction products; and the oxygenation
of the cracked products. Most sources of cellulose also contain a
significant amount of lignin, aquatic biomass such as algae being a
notable exception. The presence of lignin in the biomass further
complicates the reaction scheme to liquid fuels because lignin is
chemically very different from cellulose and behaves very differently in
the conversion reactions.

[0005] European patent application EP 0 366 138 A2 proposes a process for
manufacturing fuel from ligno-cellulose material. The document describes
a three step process. In the first step, called the digestion step,
lignin is reacted with SO2. In the second step the reacted lignin is
dissolved in an alkaline solution. The remaining cellulose is subjected
to a cracking reaction at high temperature in the presence of a molecular
sieve catalyst.

[0006] U.S. published patent application 2003/0115792 A1 discloses a
process for converting lignin into high octane blending components. The
document describes a two-step process. In the first step, lignin is
subjected to base catalyzed depolymerization. The catalyst is a dilute
solution of sodium hydroxide, or a solid super base for example CsX-type
zeolite, or a mixture of the two. In the second step, the depolymerized
lignin is subjected to a hydro-processing step comprising simultaneous
exhaustive hydro-de-oxygenation and mild hydro-cracking. The catalyst
used in the second step is a traditional hydro-treatment catalyst.

[0007] Demirbas, A, "Partly chemical analysis of liquid fraction of flash
pyrolysis products from biomass in the presence of sodium carbonate",
Energy Conversion and Management 43 (2002) 1801-1809, describes
experiments done on various types of biomass material. The addition of
sodium carbonate as catalyst increases the yield of methanol.

[0008] The described processes tackle the complexity of the reaction feed
either by proposing a multi-step process, or by focusing on a single
aspect of the conversion.

[0009] Thus, there is a particular need for a catalyst system that can be
used in a single step process for conversion of biomass to liquid fuel.

BRIEF SUMMARY OF THE INVENTION

[0010] The present invention addresses these problems by providing a
process for the catalytic pyrolysis of cellulosic biomass, said process
comprising heating the cellulosic biomass to a conversion temperature in
the range of from 200° C. to 500° C. in the presence of a
catalyst system, characterized in that the catalyst system comprises a
basic functionality, said basic functionality comprising an alkali metal
component and a multivalent metal component.

[0011] The catalyst system may further comprise an acidic component, in
particular a solid acid.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0012] The following is a description of certain embodiments of the
invention, given by way of example only.

[0013] It is desirable to provide a conversion process for biomass in
which both cellulose and lignin are converted in the same reaction step.
It is also desirable to provide a process for conversion of biomass in
which the depolymerization and cracking of cellulose take place in the
same reaction step.

[0014] It has now been found that these objectives can be achieved by
providing a catalytic pyrolysis process in which a catalyst system is
used comprising a basic functionality, said basic functionality
comprising an alkali metal component and a multivalent metal component.

[0015] The multivalent component may comprise a divalent metal, a
trivalent metal, or a combination of a divalent metal and a trivalent
metal. Suitably, the multivalent metal component comprises a
hydrotalcite, a hydrotalcite- like material, an anionic clay, a mixed
metal oxide, or a mixture thereof

[0016] In a preferred embodiment the alkali metal component comprises an
alkali metal carbonate. The alkali metal component and the multi-valence
metal component may be present in separate catalyst particles, or they
may be combined in a single catalyst particle. It is advantageous to
carry out the catalytic pyrolysis in a fluid bed reactor. If a fluid bed
reactor is used, the catalyst particles should have a shape and size to
be readily fluidized. Preferred are catalyst particles in the form of
microspheres having a particle size in the range of 100 μm to 3000
μm.

[0017] It is believed that the basic functionality of catalyst system
primarily acts on the depolymerization reaction. It is desirable to also
provide, within the catalyst system, a cracking functionality. Therefore,
a preferred embodiment of the catalyst system further comprises an acidic
component. Suitably, the acidic component comprises a solid acid.
Examples of suitable acidic components include zeolites, silica-alumina,
and combinations thereof. Particularly suitable zeolites include
ZSM-zeolite, Y-zeolite, and mixtures thereof. Particularly preferred
herein are catalyst systems comprising zeolite ZSM-5.

[0018] The conversion temperature in the process of invention is in the
range of from 250° C. to 400° C., preferably from
300° C. to 380° C. Preferably, the cellulosic biomass is
heated to the conversion temperature in a fluid bed reactor. Suitably, at
least part of the catalyst system is used as a heat carrier in the fluid
bed reactor.

[0019] As indicated above, the basic functionality of the catalyst system
is believed to be active in the depolymerization of lignin and cellulose.
This requires interaction of the catalyst system with solid biomass
material. Although such interaction takes place in a fluid bed reactor,
it is advantageous to contact the cellulosic biomass with at least one
component of the catalyst system in a pretreatment step.

[0020] Such a pretreatment step can comprise impregnating the cellulosic
biomass with a solution of a component of the catalyst system. For this
embodiment of the process, it is desirable to use for the pretreatment a
catalyst component that is soluble in water and aqueous solvents, so that
an inexpensive solvent system can be used in the pretreatment step.
Suitable examples of such soluble catalyst components include sodium
carbonate and potassium carbonate.

[0021] In an alternate embodiment of the process, pretreatment is carried
out with a solid catalyst component by mechanically treating the
cellulosic biomass in the presence of the catalyst component in
particulate form. The mechanical treatment can comprise milling,
grinding, kneading, or a combination thereof.

[0022] The cellulosic biomass for use in the present process can be of
aquatic origin, for example algae. Aquatic plants are far more efficient
at converting solar energy to biomass than are land-based plants. For
this reason, aquatic plants are a highly attractive energy crop.

[0023] In alternative embodiments, the cellulosic biomass is formed by
land-based plants. Land-based plants virtually without exception form a
combination of lignin and cellulose, commonly referred to as
ligno-cellulosic biomass. Although food crops can be used for use in the
process of the present invention, it is economically and ethically
referred to use energy crop material, agricultural waste material, or
forestry waste material. Examples of suitable energy crop materials
include switch grass and fast-growing woods, such as willow and poplar.

[0025] It will be understood that the catalyst system used in the process
of the invention is suitably in the form of particles. As mentioned
above, the catalyst particles may comprise all components of the catalyst
system. Alternatively, different components of the catalyst system may be
present in different particles.